WASHINGTON (NYTIMES) - A state lawmaker from West Virginia, a 70-year-old Alabamian armed with jars of petrol and a man who broke into Speaker Nancy Pelosi's office and posed at her desk were among those arrested after the storming of the US Capitol, federal law enforcement officials announced on Friday (Jan 8) as they promised an exhaustive investigation into the violence.

The sweeping investigation took shape after a security breakdown two days earlier allowed hundreds of people backing President Donald Trump's efforts to overturn the election results to rush into the Capitol in a deadly rampage. The debacle prompted sharp recriminations and the firings of top officials who were entrusted with protecting lawmakers. Dozens have been arrested, including 13 who face federal charges.

Law enforcement officials also backed off a suggestion that Mr Trump could face criminal charges for inciting the riot after a top prosecutor had said a day earlier that investigators were examining anyone involved, "not only" the rioters.

"Don't expect any charges of that nature," a top prosecutor in the US Attorney's Office in Washington, Mr Ken Kohl, told reporters in a telephone briefing Friday.

Law enforcement officials also sought to explain the security failure, saying that they had no indication that the day would turn violent.

But Trump supporters had for weeks openly discussed on social media their plans to protest against Congress' certification of the Electoral College results, a typically ceremonial affair, and in some cases pledged to fight for their cause.

The number of arrests is likely to grow quickly as investigators pore over social media to identify the rioters. And some could face more serious charges, including in the death of Mr Brian D. Sicknick, a Capitol Police officer who was overpowered by rioters who, according to two law enforcement officials, struck his head with a fire extinguisher. He was rushed to the hospital and died on Thursday.

Hundreds of prosecutors and FBI agents have been assigned to work on the investigation and were pursuing dozens of cases, Mr Kohl said.

"We are far from done," said Steven M. D'Antuono, who runs the FBI's Washington Field Office.

He also rebutted the notion of any involvement in the violence by left-wing anti-fascist agitators, whom Mr Trump's supporters have falsely tried to blame.